Ayres appeared in more than 60 films, but is known for being a conscientious objector to World War II. Both Hollywood and movie fans balked at his refusal to fight in the war, and his career ground to a halt. Later in the war, he volunteered to serve as a medic and chaplain's aide, resurrecting his film career. His film credits include All Quiet on the Western Front, The Kiss, and Johnny Belinda. He also appeared in nine films as Dr. Kildare.